A0

A0, A-0, A0, or a0 may refer to:


 * 101 A0 and 103 A0, two versions of the German Heinkel Tourist moped
 * A0 paper size, an international ISO 216 standard paper size (841 × 1189 mm), which results in an area very close to 1 m2
 * A0 highway (Zimbabwe), a highway which orbits Zimbabwe
 * A0, the lowest A (musical note) note on a standard piano
 * A0, a climbing grade
 * A00, Irregular chess openings code in the Encyclopaedia of Chess Openings
 * A00, an unofficial paper size twice the size of A0 paper size
 * A-0 Geyser, a geyser in Yellowstone National Park
 * A-0 System, an early compiler related tool developed for electronic computers
 * L'Avion, IATA airline designator for the French airline
 * Characters of type A0, an older term for algebraic Hecke characters
 * a0, the accepted mathematical symbol for the Bohr radius
 * Haplogroup A00 and A0; see Y-chromosomal Adam and Haplogroup A (Y-DNA)
 * A0, a subdivision in stellar classification
 * A0, sometimes written as 0xA0, is the hexadecimal representation of non-breaking space in various character encoding standards
 * A0 road (Sri Lanka), an A-Grade road in Sri Lanka

Airplanes and rockets

 * A-0, a 1943 Pre-production model of the German Walter HWK 509 liquid-fuel bipropellant rocket engine
 * A-0, a 1938 variant of the German Siebel Si 204 transport and trainer aircraft
 * He 177 A-0, a pre-production series of the 1942 German Heinkel He 177 heavy bomber
 * Hs 126A-0, a variant of the 1937 German Henschel Hs 126 reconnaissance aircraft
 * Ju 87 A-0, a variant of the 1936 German Junkers Ju 87 dive bomber aircraft
 * Me 210A-0, a pre-production variant of the 1943 German Messerschmitt Me 210 heavy fighter aircraft

Submarine

 * Isaac Peral (A-0), a Spanish submarine